1. Field of the Invention
The present invention relates to an alternator used in an automotive alternator driven by an internal combustion engine, for example.
2. Description of the Related Art
FIG. 20 is a cross section of a conventional automotive alternator, FIG. 21 is a view of the internals at a rear bracket end of the automotive alternator in FIG. 20, FIG. 22 is a perspective of a rotor of the alternator in FIG. 20, and FIG. 23 is a perspective of a stator of the alternator in FIG. 20.
This alternator includes: a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2; a shaft 6 disposed inside the case 3, a pulley 4 being secured to a first end of the shaft 6; a Lundell-type rotor 7 secured to the shaft 6; first and second fans 5a and 5b secured to first and second end surfaces of the rotor 7; a stator 8 secured to an inner wall within the case 3; slip rings 9 secured to a second end of the shaft 6 for supplying electric current to the rotor 7; a pair of brushes 10 which slide on surfaces of the slip rings 9; wires 17 each having an end portion connected to these brushes 10; springs 16 for pressing the brushes 10 toward the slip rings 9; a brush holding assembly 100 having a holding portion 11a for housing the brushes 10 and a cover 11b removably disposed on a head portion of the holding portion 11a; a rectifier 12 which is electrically connected to the stator 8 for converting alternating current generated in the stator 8 into direct current; a regulator 13 secured to the brush holding assembly 100 for adjusting the magnitude of an alternating voltage generated in the stator 8; and a cooling plate 14 placed in contact with and secured to the regulator 13 to dissipate and cool heat generated in the regulator 13.
The rotor 7 includes: a rotor coil 18 for generating magnetic flux on passage of electric current; and a pole core 19 disposed so as to cover the rotor coil 18, magnetic poles being formed in the pole core 19 by the magnetic flux. The pole core 19 is constituted by a first pole core portion 20 and a second pole core portion 21 which intermesh with each other. The first pole core portion 20 is made of iron and has tapered first claw-shaped magnetic poles 22 extending axially. The second pole core portion 21 is made of iron and has tapered second claw-shaped magnetic poles 23 extending axially in an opposite direction to the first claw-shaped magnetic poles 22.
The stator 8 is constituted by: a stator core 24 for passage of a rotating magnetic field from the rotor coil 18, the stator core being formed by laminating a plurality of steel plates together; and three stator winding phase portions 25 through each of which an output current flows. The stator core 24 is constituted by an annular core back 26, and a plurality of teeth 27 extending radially inwards from the core back 26 at an even pitch in a circumferential direction. The stator winding phase portions 25, formed by winding an enamel-coated conducting wire for a plurality of winds, are housed in a total of thirty-six slots 28 formed between adjacent pairs of the teeth 27.
In an automotive alternator of the above construction, electric current is supplied from a battery (not shown), which is an electric power supply, through the brushes 10 and the slip rings 9 to the rotor coil 18, generating magnetic flux and giving rise to a magnetic field. At the same time, since the pulley 4 is driven by the engine and the rotor 7 is rotated by the shaft 6, a rotating magnetic field is applied to the stator core 24, generating electromotive force in the stator winding phase portions 25 and an output current is generated by an external load connected to the automotive alternator.
Moreover, after the commencement of power generation, the alternator is switched over to self-excitation, in which a portion of the electric current output from the alternator, rather than from the battery, is supplied through the brushes 10 to the rotor coil 18.
In an automotive alternator of the above construction, one problem has been that the brush holding assembly 100 is housed in the sealed case 3, and when replacing expended brushes 10, for example, the automotive alternator must first be disassembled and the brush holding assembly 100 removed from the case 3. Then the operation of replacing the brushes 10 is performed, and after that, the brush holding assembly 100 must be installed in the case 3 and the automotive alternator reassembled.
The present invention aims to solve the above problem and an object of the present invention is to provide an alternator that facilitates the operation of replacing the brushes, which alternator has improved cooling efficiency and a small size.
In order to achieve the above object, according to one aspect of the present invention, there is provided an alternator including:
a case;
a shaft passing through the case;
a rotor secured to the shaft, the rotor including a rotor coil for generating a magnetic flux on passage of an electric current therethrough, and a plurality of claw-shaped magnetic poles extending in an axial direction and covering said rotor coil, the claw-shaped magnetic poles being magnetized into North-seeking (N) and South-seeking (S) poles by the magnetic flux;
a stator including a stator core provided with a plurality of slots formed so as to extend axially and be spaced circumferentially, and a stator winding mounted to the stator core;
slip rings secured to the shaft;
brushes the end of which slide on the slip rings, supplying electric current to the rotor coil through the slip rings from an electric power supply;
a brush holding assembly which the shaft passes through, the brush holding assembly holding the brushes within a holding portion and provided with a cover capable of being opened to remove the brushes; and
a cap for closing an open portion for removal and insertion of the brushes, the open portion being formed at a position on the case facing the cover.
The brush holding assembly may extend to a vicinity of the open portion.
A regulator for adjusting the magnitude of an alternating voltage generated in the stator and a cooling plate placed in contact with the regulator may be disposed on the brush holding assembly so as to overlap each other on the non-rotor side of the brush holding assembly.
The cooling plate may be provided with plural cooling fins extending in a radial direction of the rotor.
A partition wall for making the cooling air passing through the cooling plate take a circuitous route toward the brush may be provided.
The partition wall may be formed so as to be integral with the cap.
A cooling fan to generate forced convection in the case may be provided between the rotor and the brush holding assembly.
A conducting wire of the stator winding may extend outwards in an axial direction from an end surface of the stator core and be formed into coil ends having a uniform shape in a circumferential direction.